Hydrogen embrittlement of Aluminum-Lithium alloys

The objective of this work is to study the effects of dissolved hydrogen on the mechanical properties of aluminum-lithium alloys: 2090, 2091, and Weldalite 049, and to compare with the effects on aluminum-copper 2219 alloy. Prior to mechanical testing, aging studies were performed for 2090 and 2219 using microhardness Vickers to determine the peak aged condition required by NASA. The Charpy tests are part of this study designed to investigate the effects of temperature and notch orientation on fracture behavior. Disk rupture tests were used with various gases (hydrogen and nitrogen) and three strain rates (increment of 50 psi every 20, 200 and 300 seconds) and two temperatures (room and liquid nitrogen temperatures) to determine the effects of hydrogen on the sample during the tests. Some independent studies on the corrosion behavior and electrochemical hydrogen charging of 2219 and 2090 were also performed.

An effect of double peak aged condition was found for both 2219 and 2090 alloys. Prior to mechanical testing, the 2090 received in the T3 or W51 conditions was chosen to be aged in an air furnace at 170°C for 16 hours. The Charpy studies showed a higher propagation energy needed for the T-S and L-S orientations than for the L-T and T-L orientations, due in large part to the extensive delamination propagation of the fracture. The disk rupture tests showed a important decrease of the fracture to failure on the 2090 and 2091 due to hydrogen while no important variations were seen for the 2219 and the weldalite 049 alloys. No effect of hydrogen were found, with the disk rupture test, at cryogenic temperature and for all alloys. The corrosion behavior of 2219, as well as 2090, showed development of pits under neutral and acidic environments while general corrosion was obtained with basic environment. Two solutions were found to charge the samples in hydrogen: a potentiostatic test for 5 hours at -3V, and a galvanostatic test for 20 hours at -500μA, both performed in a 0.04 N HCl plus As₂O₃ environment.